Fig. 3: Revisiting the contribution of humic substances to in situ iron-binding ligands.
From: Marine biogenic humic substances control iron biogeochemistry across the Southern Ocean
a Electroactive humic substances (eHS, a) and b their potential iron saturation level (DFe:eHS ratio) as reported for different aquatic systems. Iron saturation levels for Suwanee River fulvic acid (FA, blue line) and humic acid (HA, brown line) are shown on (b). For aquatic systems where both eHS and iron-binding ligand (Fe-L) were available, the relative contribution of eHS to the Fe-L pool was calculated using either Suwanee River FA (c) or HA (d) iron-binding capacity, as in refs. 14,21. The 100% contribution of humics to in situ Fe-L is shown with a dotted line. Data are represented as box plots with mean and 5th and 95th percentiles. Standard deviations are shown as error bars and the number of observations is listed in brackets next to the corresponding marine region: 1, Arctic20,21; 2, North Atlantic14,22; 3, North Pacific14; 4, Mediterranean Sea22,29; 5, South Pacific19,24; and 6, Southern Ocean14 (mostly this study), n = 106 for (a and b), n = 70 for (c and d).
